FIG. 1 depicts a schematic diagram of teleconference system 100 in the prior art. System 100 comprises telecommunications endpoints 101-1 through 101-J, wherein J is an integer greater than one; private branch exchange (PBX) 102; telecommunications network 103; and teleconference bridge 104, interconnected as shown.
Telecommunications endpoint 101-j, where j has a value between 1 and J, inclusive, is capable of handling a telephone call for its user. Endpoint 101-j is able to call, or to be called by, another endpoint. In order to participate in a conference call, endpoint 101-j is able to dial a telephone number that routes to teleconference bridge 104. Endpoint 101-j can be a cellular phone, a conference phone (i.e., “speakerphone”), a deskset, or some other type of telecommunications appliance.
Some of endpoints 101-1 through 101-J are PBX terminals, such as those in an office enterprise network, for which telecommunications service is enabled by private branch exchange 102.
Telecommunications network 103 provides the connectivity among endpoints 101-1 through 101-J, exchange 103, and teleconference bridge 104. Telecommunications network 103 comprises a transmission network—for example, the Public Switched Telephone Network, which is a complex of telecommunications equipment that is owned and operated by different entities throughout the World. Network 103 can also comprise the Internet or possibly other Internet Protocol-based networks.
Teleconference bridge 104 is a server or switch that enables the users of multiple endpoints to communicate with each other during a conference call. Bridge 104 receives audio signals from endpoints that are participating on a conference call, mixes those signals together, and transmits the mixed signals back to the endpoints.
As depicted in FIG. 1, system 100 is a traditional teleconferencing system for J teleconference locations, where a location is defined by a single endpoint (i.e., endpoint 101-j), supported by a teleconference bridge (i.e., bridge 104). Some of the endpoints are speakerphones, which are designed specifically to handle conference call communication. Each speakerphone is connected to the bridge via a monophonic, bi-directional channel. If any given speakerphone at a teleconference location has multiple feeds—that is, a main microphone and one or more satellite microphones, or a main loudspeaker and one or more satellite loudspeakers—they are combined at the speakerphone itself into the monophonic channel transmitted by that speakerphone to the bridge. This is depicted in FIG. 2, showing an overhead view in which endpoint 101-11 is situated on table 202 of conference room 201. Endpoint 101-11, a speakerphone, comprises satellite microphones 203-1 and 203-2, as well as loudspeaker 204.
During operation, the monophonic feed from each endpoint, such as endpoint 101-11, is fed into bridge 104, which adds the feeds, and the sum is distributed by the bridge back to the speakerphones at the other locations. Each speakerphone at each location receives a signal via a monophonic channel from the bridge, which signal is played out of all loudspeakers connected to that speakerphone. In the operation of any such traditional bridge, the monophonic signal received by any endpoint 101-j contains components of one or more other endpoints 101-k, k≠j, but explicitly excludes components of the signal sent to the bridge by endpoint 101-j. By doing so, bridge 104 prevents regenerative acoustic feedback that would otherwise occur.
Each monophonic, bi-directional channel is associated with a phone line that terminates at the conference bridge. From the bridge's perspective, each channel and line equates to a different “location,” even though conference call participant who are using a speakerphone and a participant who is using a cell phone might be present in the same conference room.